Display articles with diffractive, antiglare surfaces and methods of making the same

ABSTRACT

A display article is described herein that includes: a substrate comprising a thickness and a primary surface; and the primary surface having defined thereon a diffractive surface region. The diffractive surface region comprises a plurality of structural features that comprises a plurality of different heights in a multimodal distribution. Further, the substrate exhibits a sparkle of less than 4%, as measured by pixel power deviation (PPD 140 ) at an incident angle of 0° from normal, a distinctness of image (DOI) of less than 80% at an incident angle of 20° from normal, and a transmittance haze of less than 20% from an incident angle of 0° from normal.

This application claims the benefit of priority under 35 U.S.C. § 119 of U.S. Provisional Application Ser. No. 63/049,843 filed on Jul. 9, 2020, the content of which is relied upon and incorporated herein by reference in its entirety.

FIELD

The present disclosure generally relates to display articles with diffractive, antiglare surfaces and methods of making the same, particularly display articles comprising a substrate with one or more primary surfaces with a diffractive surface region and antiglare characteristics.

BACKGROUND

Antiglare surfaces are often used in display devices such as LCD screens, tablets, smartphones, OLEDs and touch screens to avoid or reduce specular reflection of ambient light. In many display devices, these antiglare surfaces are formed by providing a level of roughness to one or more surfaces of the glass and/or films on the glass to spread and scatter incident light. Antiglare surfaces in the form of a roughened glass surface are often used on the front surfaces of these display devices to reduce the apparent visibility of external reflections from the display and improve readability of the display under differing lighting conditions.

Conventional approaches for imparting antiglare properties on glass substrates employed in display articles have been successful to a certain degree. Typically, these approaches have been used to employ a randomized surface roughness profile in the surfaces of the substrate and/or within films on such substrates. These approaches, however, have resulted in glass substrates and display articles with high haze and/or high display sparkle. The high haze levels can reduce display contrast by scattering high-angle light towards the user, making black levels appear ‘washed out’. The high display sparkle levels are unwanted random variations in pixel brightness resulting in a grainy appearance that shifts with viewing angle.

In view of these considerations, there is a need for display articles and substrates with improved antiglare characteristics that include, but are not limited to, the suppression of specular reflection, low sparkle and low distinctness of image. There is also a need for methods of making such display articles and substrates.

SUMMARY

According to an aspect of the disclosure, a display article is provided that includes: a substrate comprising a thickness and a primary surface; and the primary surface having defined thereon a diffractive surface region. The diffractive surface region comprises a plurality of structural features that comprises a plurality of different heights in a multimodal distribution. Further, the substrate exhibits a sparkle of less than 4%, as measured by pixel power deviation (PPD₁₄₀) at an incident angle of 0° from normal, a distinctness of image (DOI) of less than 80% at an incident angle of 20° from normal, and a transmittance haze of less than 20% from an incident angle of 0° from normal.

According to an aspect of the disclosure, a display article is provided that includes: a substrate comprising a thickness and a primary surface; and the primary surface having defined thereon a diffractive surface region. The diffractive surface region comprises a plurality of structural features comprising a pitch of less than 125 μm and a fill fraction from 30% to 70%, each structural feature comprising a diameter of less than 100 μm. Further, the substrate exhibits a sparkle of less than 4%, as measured by pixel power deviation (PPD₁₄₀) at an incident angle of 0° from normal, a distinctness of image (DOI) of less than 80% at an incident angle of 20° from normal, and a transmittance haze of less than 20% from an incident angle of 0° from normal.

According to an aspect of the disclosure, a display article is provided that includes: a substrate comprising a thickness and a primary surface; and the primary surface having defined thereon a diffractive surface region. The diffractive surface region comprises a plurality of structural features comprising a pitch of less than 125 μm, a fill fraction from 30% to 70%. Further, each structural feature comprises a height or depth of from 50 nm to 250 nm. In some cases, the plurality of structural features further comprises a non-random spatial distribution.

According to another aspect of the disclosure, a method of making a display article is provided that includes: masking a substrate comprising a thickness and a primary surface with a mask; forming a diffractive surface region within the primary surface of the substrate; and removing the mask from the substrate. The diffractive surface region comprises a plurality of structural features that comprises a plurality of different heights in a multimodal distribution. Further, the plurality of structural features further comprises a first portion of structural features at a first average height and a second portion of structural features at a second average height. In addition, the substrate exhibits a sparkle of less than 4%, as measured by pixel power deviation (PPD₁₄₀) at an incident angle of 0° from normal, a distinctness of image (DOI) of less than 80% at an incident angle of 20° from normal, and a transmittance haze of less than 20% from an incident angle of 0° from normal.

Additional features and advantages will be set forth in the detailed description which follows, and will be readily apparent to those skilled in the art from that description or recognized by practicing the embodiments as described herein, including the detailed description which follows, the claims, as well as the appended drawings.

It is to be understood that both the foregoing general description and the following detailed description are merely exemplary, and are intended to provide an overview or framework to understanding the nature and character of the disclosure as it is claimed.

The accompanying drawings are included to provide a further understanding of principles of the disclosure, and are incorporated in, and constitute a part of, this specification. The drawings illustrate one or more embodiment(s) and, together with the description, explain, by way of example, principles and operation of the disclosure. It is to be understood that various features of the disclosure disclosed in this specification and in the drawings can be used in any and all combinations.

BRIEF DESCRIPTION OF THE DRAWINGS

These and other features, aspects and advantages of the present disclosure are better understood when the following detailed description of the disclosure is read with reference to the accompanying drawings, in which:

FIG. 1A is a cross-sectional, schematic view of a display article, according to an embodiment of the disclosure.

FIG. 1B is a cross-sectional, schematic view of a display article, according to an embodiment of the disclosure.

FIG. 1C is a cross-sectional, schematic view of a display article with an antireflective coating, according to an embodiment of the disclosure.

FIG. 2 is a cross-sectional, schematic view of a diffractive antiglare structure, according to an embodiment of the disclosure.

FIGS. 3A and 3B are plots of diffraction efficiency in reflection and transmission, respectively, as a function of structure depth for the diffractive antiglare structure depicted in FIG. 2, according to embodiments of the disclosure.

FIGS. 4A-4C are plots of diffraction efficiency in reflection as a function of structure depth for the diffractive antiglare structure depicted in FIG. 2 at fill fractions of 15%, 30% and 70%, respectively, according to embodiments of the disclosure.

FIG. 5 is a plot of diffraction efficiency in reflection as a function of structure depth for the diffractive antiglare surface depicted in FIG. 2 with varying incident light wavelengths, according to embodiments of the disclosure.

FIG. 6 is a schematic flow chart of a method of making a display article, according to an embodiment of the disclosure.

FIGS. 7A-7D are optical micrographs of diffractive surface regions of substrates employed in display articles, according to embodiments of the disclosure.

FIG. 8 is a plot of etch depth as a function of etch time to form two structural features of diffractive surface regions of substrates employed in display articles, according to embodiments of the disclosure.

FIGS. 9A and 9B are plots of distinctness of image (DOI) as a function of etch depth for structural features having different sizes and fill fractions, as part of diffractive surface regions of substrates employed in display articles, according to embodiments of the disclosure.

FIGS. 10A and 10B are plots of pixel power deviation (PPD₁₄₀) and haze as a function of etch depth for structural features having different sizes and fill fractions, as part of diffractive surface regions of substrates employed in display articles, according to embodiments of the disclosure.

FIGS. 10C and 10D are plots of pixel power deviation (PPD₁₄₀) and haze as a function of etch depth for structural features having different sizes and fill fractions, as part of diffractive surface regions of substrates employed in display articles, according to embodiments of the disclosure.

FIG. 11A is an optical image and surface height distribution bar of a diffractive surface region with a first set of structural features having a depth of about 150 nm and a fill fraction of about 50%, according to an embodiment of the disclosure.

FIG. 11B is an angular plot with amplitude of reflectance vs. reflectance angle in degrees for three articles having differing diffractive surface regions, according to embodiments of the disclosure.

FIG. 12 is an angular plot with amplitude of reflectance vs. reflectance angle in degrees for a display article having a diffractive surface region, according to an embodiment of the disclosure.

FIGS. 13A and 13B are optical images of a display article with a diffractive surface region, before and after removal of a mask and etchant employed in a method of making a display article, according to an embodiment of the disclosure.

FIG. 14 is a plot of distinctness of image (DOI) as a function of etch depth for structural features of a diffractive surface region of a display article, according to an embodiment of the disclosure.

FIG. 15 is a schematic plot of seven structural features of a diffractive surface region, as arranged in a hexagonal pattern to depict hexagonality (H), according to an embodiment of the disclosure.

FIGS. 16A and 16B are nearest neighbor distribution and pattern periodogram plots, respectively, of a diffractive surface region of a display article, according to an embodiment of the disclosure.

FIGS. 17A and 17B are nearest neighbor distribution and pattern periodogram plots, respectively, of a diffractive surface region of a display article, according to an embodiment of the disclosure.

DETAILED DESCRIPTION

In the following detailed description, for purposes of explanation and not limitation, example embodiments disclosing specific details are set forth to provide a thorough understanding of various principles of the present disclosure. However, it will be apparent to one having ordinary skill in the art, having had the benefit of the present disclosure, that the present disclosure may be practiced in other embodiments that depart from the specific details disclosed herein. Moreover, descriptions of well-known devices, methods and materials may be omitted so as not to obscure the description of various principles of the present disclosure. Finally, wherever applicable, like reference numerals refer to like elements.

Ranges can be expressed herein as from “about” one particular value, and/or to “about” another particular value. When such a range is expressed, another embodiment includes from the one particular value and/or to the other particular value. Similarly, when values are expressed as approximations, by use of the antecedent “about,” it will be understood that the particular value forms another embodiment. It will be further understood that the endpoints of each of the ranges are significant both in relation to the other endpoint, and independently of the other endpoint.

Directional terms as used herein—for example “up,” “down,” “right,” “left,” “front,” “back,” “top,” “bottom”—are made only with reference to the figures as drawn and are not intended to imply absolute orientation.

Unless otherwise expressly stated, it is in no way intended that any method set forth herein be construed as requiring that its steps be performed in a specific order. Accordingly, where a method claim does not actually recite an order to be followed by its steps, or it is not otherwise specifically stated in the claims or descriptions that the steps are to be limited to a specific order, it is in no way intended that an order be inferred, in any respect. This holds for any possible non-express basis for interpretation, including: matters of logic with respect to arrangement of steps or operational flow; plain meaning derived from grammatical organization or punctuation; the number or type of embodiments described in the specification.

As used herein, the singular forms “a,” “an” and “the” include plural referents unless the context clearly dictates otherwise. Thus, for example, reference to a “component” includes aspects having two or more such components, unless the context clearly indicates otherwise.

Aspects of the disclosure generally pertain to display articles with diffractive, antiglare surfaces and methods of making the same, particularly display articles comprising a substrate with one or more primary surfaces with a diffractive surface region and antiglare characteristics. In general, the display articles and substrates of the disclosure employ an engineered diffractive surface region with antiglare properties, such as low distinctness of image (DOI), low pixel power deviation (PPD₁₄₀) and low transmitted haze. Each of these antiglare properties is desirable for display applications, and conventional approaches have not achieved this combination of antiglare properties. The diffractive surface regions, according to aspects of the disclosure, possess structural features, such as holes and/or pillars, with a diameter of less than 100 μm, a pitch of less than 125 μm and a fill fraction of 40 to 55%. The diffractive surface regions, as including these holes and/or pillars, can enable the display articles employing them to exhibit a first-surface reflectance DOI of less than 80%, a PPD₁₄₀ of less than 4%, and a transmitted haze of less than 20%. Further, these properties are achievable without the additional presence of any antireflective coating structures over the diffractive surface region. Further, the diffractive surface region, in some embodiments, can have a multimodal distribution (e.g., a bimodal distribution) of surface heights with a height and/or depth of from 120 to 200 nm, which can reduce specular reflectance through diffractive interference.

The display articles of the disclosure, as including a diffractive surface region, offer several advantages over display articles with conventional approaches to achieving antireflective characteristics. For example, the display articles of the disclosure can suppress specular reflectance by a factor of 10× or more using diffractive light scattering, while also achieving a combination of low haze, low sparkle and high mechanical durability. The high mechanical durability is associated with the relatively low aspect ratio of the structural features of the diffractive surface region. In addition, some display articles according to the disclosure employ a diffractive surface region and a multilayer antireflective coating structure to achieve specular reductions of greater than 20×, 50× or even 100×. Another advantage of the display articles of the disclosure is that the planar step-like and semi-planar morphology, together with the controlled structure depths of less than 1 micron, or less than 250 nm, of the diffractive surface region allows them to be easily fabricated with much lower consumption of glass material and etching chemicals (such as HF) compared to conventional etched, antiglare glass substrates, leading to less environmental waste and potential cost benefits. Various processes can be employed to create these structures (e.g., organic mask and etching, organic mask and vapor deposition, organic mask and liquid phase deposited oxide), which can aid in maintaining low manufacturing costs. A further advantage of these display articles is that they can exhibit a combination of antiglare, optical properties not achievable from conventional antiglare approaches. For example, the display articles of the disclosure, as incorporating a diffractive surface region, have achieved a DOI of less than 80%, a PPD₁₄₀ of less than 2% and a haze of less than 5%.

Referring to FIGS. 1A and 1B, a display article 100 is depicted as including a substrate 10 with a plurality of primary surfaces 12 and 14, and a thickness 13. The primary surface 12 of the substrate 10 also includes a diffractive surface region 30 a. Hence, the primary surface 12 has a diffractive surface region 30 a defined thereon such that the diffractive surface region 30 a is formed from or otherwise part of the substrate 10, as shown in FIG. 1A. In some implementations (not shown), a diffractive surface region 30 a can also be defined by the primary surface 14 of the substrate 10. Further, in some implementations, the diffractive surface region 30 a is defined by both of primary surfaces 12 and 14. As also depicted in FIG. 1A, the diffractive surface region 30 a includes a plurality of structural features 20 that comprises a plurality of different heights and/or depths in a multimodal distribution.

Referring again to the diffractive surface region 30 a shown in FIGS. 1A and 1B, it can describe a surface comprised of circular pillars or holes (i.e., the structural features 20) with a fixed set of a few possible discrete height or depth levels above or below the primary surface 12 of the substrate 10. Each feature 20, in some instances, can have a planar top characterized by a single height or depth. These features 20 may have the same or a finite number of different diameters. The placement of the features 20 can be random, but this is by design or otherwise purposely engineered and not a random function of the manufacturing process. The manufacturing process can use some form of precision, engineered masking to produce the designed feature shapes exactly (to within some tolerance). As used herein, a diffractive surface region 30 a with a plurality of structural features 20 (as shown in exemplary form in FIGS. 1A and 1B) with a plurality of different heights in a “multimodal distribution” means that diffractive surface region consists primarily of two (e.g., a bimodal distribution), three (e.g., a trimodal distribution), four, five or more distinct and purposely engineered average or primary heights, and each of these average or primary heights consists of distributions whose widths are less than or comparable to the vertical separation between the heights. Referring again to FIGS. 1A and 1B, the exemplary diffractive surface region 30 a comprises a plurality of heights and/or depths in a bimodal distribution. Further, as used herein, a “bimodal distribution” means that diffractive surface region consists primarily of two distinct and purposely engineered average or primary heights, and each of these average or primary heights consists of distributions whose widths are less than or comparable to the vertical separation between the heights.

In embodiments, the plurality of structural features 20 includes pillars and/or holes and these pillars and/or holes make up a multimodal distribution of surface heights and/or depths. According to some implementations, the diffractive surface region 30 a can comprise a two-dimensional array of circular, square, hexagonal, polygonal, or irregular structural features 20. Further, these structural features 20 can be arranged in an ordered or a semi-ordered array—essentially, any of various array schemes that are reproducibly fabricated and do not depend on manufacturing process randomness for their function. As such, in some embodiments of the display article 100 depicted in FIGS. 1A and 1B, the diffractive surface region 30 a comprises a plurality of structural features 20 that comprises a plurality of different heights in a multimodal distribution and is distributed across the surface region 30 a in a semi-ordered or an ordered array.

Referring again to the display article 100 of FIGS. 1A and 1B, the substrate 10 can exhibit a sparkle of less than 4%, as measured by PPD₁₄₀ at an incident angle of 0° from normal. The substrate 10 can also exhibit a DOI of less than 80% at an incident angle of 20° from normal. Further, the substrate 10 of the display article 100 can exhibit a transmittance haze of less than 20% from an incident angle of 0° from normal. Embodiments of the display article 100 depicted in FIGS. 1A and 1B can also exhibit a combination of these optical properties.

According to some implementations of the display article 100 depicted in FIGS. 1A and 1B, the multimodal distribution of the diffractive surface region 30 a further includes a first portion of structural features 22 a, 22 a′ at a first average height 24 a (or, interchangeably referred to as a first average depth 24 a) and a second portion of structural features 22 b, 22 b′ at a second average height 24 b (or, interchangeably referred to as a first average depth 24 b). According to embodiments of the display article 100, the first portion of structural features 22 a, 22 a′ can be pillars 22 a, as shown in exemplary form in FIG. 1A. According to embodiments of the display article 100, the first portion of structural features 22 a, 22 a′ can be holes 22 a′, as shown in exemplary form in FIG. 1B. According to some of these embodiments, from a structural standpoint, the second portion of structural features 22 b, 22 b′ can be a set of ligaments 22 b (e.g., as shown in FIG. 1A situated between the pillars 22 a) or mesas 22 b′ (e.g., as shown in FIG. 1B situated between the holes 22 a′) between the first portion of structural features 22 a, 22 a′. According to implementations, the ligaments 22 b can be the ligaments, matrix or other comparable structure between the first portion of the structural features 22 a, 22 a′, when the first portion is configured as pillars 22 a. Further, the mesas 22 b′ can be mesas, plateaus, matrix or other comparable structure between the first portion of the structural features 22 a, 22 a′, when the first portion is configured as holes 22 a′. It should also be understood, however, that the second portion of structural features 22 b, 22 b′, like the first portion of structural features 22 a, 22 a′ includes a distribution of surface heights with a second average surface height 24 b. Further, the first average height 24 a of the pillars 22 a or the first average depth 24 a of the holes 22 a′, depending on the configuration of the diffractive surface region 30 a, can range from about 25 nm to about 300 nm, from about 50 nm to about 250 nm, from about 75 nm to about 225 nm, from about 100 nm to about 200 nm, from about 120 nm to about 180 nm, or from about 130 nm to about 170 nm.

As noted earlier, the display article 100 depicted in FIGS. 1A and 1B includes a substrate 10 with a diffractive surface region 30 a that can include a plurality of structural features 20 of different heights in a multimodal distribution. This multimodal distribution can have a plurality of surface height modes, e.g., the distribution may be bimodal (e.g., with a first portion of structural features 22 a, 22 a′ and a second portion of structural features 22 b, 22 b′), tri-modal, four-modal, five-modal, etc. In embodiments, the diffractive surface region 30 a is configured such that each of these modes is characterized by a distinct peak of surface height vs. area fraction within the distribution of surface heights. These peaks may be distinguished by a decrease in area fraction of at least 20%, at least 50% or at least 80% from the peak surface height value between the distinct peaks associated with each of the modes. Further, the peaks of each of the modes may have a varying width, and the area fraction does not need to drop to zero between the peaks of the distribution. In some embodiments, however, the area fraction for heights in between each of the peaks on a surface height vs. area chart may drop to zero or close to zero.

Referring again to the display article 100 depicted in FIGS. 1A and 1B, the multimodal distribution of the diffractive surface region 30 a can be further characterized such that the difference between the first average height 24 a and the second average height 24 b is from about 25 nm to about 300 nm, from about 50 nm to about 250 nm, from about 75 nm to about 225 nm, from about 100 nm to about 200 nm, from about 120 nm to about 200 nm, from about 120 nm to about 180 nm, or from about 130 nm to about 170 nm. For example, the difference between the first average height 24 a and the second average height 24 b can be about 25 nm, 50 nm, 75 nm, 100 nm 125 nm, 150 nm, 175 nm, 200 nm, 225 nm, 250 nm, 275 nm, 300 nm, and all height differences between the foregoing levels. In some embodiments, the difference between the first average height 24 a and the second average height 24 b may be in a range that corresponds to about ¼ of the wavelength of visible light in air, or odd multiples of the ¼ of the wavelength of visible light.

Referring again to the display article 100 depicted in FIGS. 1A and 1B, embodiments are configured such that the diffractive surface region 30 a includes a first planar region 21 a that corresponds to the first average height 24 a of the first portion of structural features 22 a, 22 a′ and a second planar region 21 b that corresponds to the second average height 24 b of the second portion of structural features 22 b, 22 b′. That is, each of the first and second planar regions 21 a and 21 b, respectively, is planar in the sense that these regions have close to the same surface height (i.e., within one mode of the surface height vs. area fraction distribution of the surface heights of the plurality of structural features 20). Further, each of these planar regions 21 a and 21 b can be characterized by a surface height variation (or roughness) within the planar region of less than 50 nm root-mean-square (RMS) variation, less than 20 nm RMS, less than 10 nm RMS, less than 5 nm RMS, less than 2 nm RMS, or less than 1 nm RMS. For example, each of these planar regions 21 a and 21 b can be characterized by a surface height variation from 0.1 nm RMS to 50 nm RMS, from 0.1 nm RMS to 20 nm RMS, from 0.1 nm RMS to 10 nm RMS, or from 0.1 nm RMS to 1 nm RMS. Further, according to some embodiments, the planar regions 21 a and 21 b can also include individual sub-regions or domains (not shown) having an average area within each domain of greater than 5 μm², greater than 10 μm², greater than 20 μm², greater than 50 μm², or greater than 100 μm².

According to some embodiments of the display article 100 depicted in FIGS. 1A and 1B, as noted earlier, the diffractive surface region 30 a can include two or more planar regions (e.g., first and second planar regions 21 a and 21 b). Further, each of these planar regions (e.g., plateaus, mesas, etc.) can be substantially planar, meaning that more than 50%, more than 80%, or more than 90% of the diffractive surface region 30 a is planar. In some embodiments, the total surface area of the first and second planar regions 21 a and 21 b is at least 50%, at least 60%, at least 70%, at least 80%, or at least 90% of a total surface area of the diffractive surface region 30 a.

According to implementations of the display article 100 depicted in FIGS. 1A and 1B, the article is characterized by a low level of sparkle. In general, the diffractive surface region 30 a associated with the substrate 10 of these articles can produce light deflections leading to an image artifact called “sparkle”, Display “sparkle” or “dazzle” is a generally undesirable side effect that can occur when introducing antiglare or light scattering surfaces into a pixelated display system such as, for example, an LCD, an OLED, touch screens, or the like, and differs in type and origin from the type of “sparkle” or “speckle” that has been observed and characterized in projection or laser systems. Sparkle is associated with a very fine grainy appearance of the display and may appear to have a shift in the pattern of the grains with changing viewing angle of the display. Display sparkle may be manifested as bright and dark or colored spots at approximately the pixel-level size scale.

As used herein, the terms “pixel power deviation” and “PPD₁₄₀” refer to the quantitative measurement for display sparkle. Further, as used herein, the term “sparkle” is used interchangeably with “pixel power deviation” and “PPD₁₄₀.” PPD₁₄₀ is calculated by image analysis of display pixels according to the following procedure. A grid box is drawn around each LCD pixel. The total power within each grid box is then calculated from charge-coupled device (CCD) camera data and assigned as the total power for each pixel. The total power for each LCD pixel thus becomes an array of numbers, for which the mean and standard deviation may be calculated. The PPD₁₄₀ value is defined as the standard deviation of total power per pixel divided by the mean power per pixel (times 100). The total power collected from each LCD pixel by the eye simulator camera is measured and the standard deviation of total pixel power (PPD₁₄₀) is calculated across the measurement area, which typically comprises about 30×30 LCD pixels.

The details of a measurement system and image processing calculation that are used to obtain PPD₁₄₀ values are described in U.S. Pat. No. 9,411,180 entitled “Apparatus and Method for Determining Sparkle,” the salient portions of which that are related to PPD measurements are incorporated by reference herein in their entirety. Further, unless otherwise noted, the SMS-1000 system (Display-Messtechnik & Systeme GmbH & Co. KG) is employed to generate and evaluate the PPD₁₄₀ measurements of this disclosure. The PPD₁₄₀ measurement system includes: a pixelated source comprising a plurality of pixels (e.g., a Lenovo Z50 140 ppi laptop), wherein each of the plurality of pixels has referenced indices i and j; and an imaging system optically disposed along an optical path originating from the pixelated source. The imaging system comprises: an imaging device disposed along the optical path and having a pixelated sensitive area comprising a second plurality of pixels, wherein each of the second plurality of pixels are referenced with indices m and n; and a diaphragm disposed on the optical path between the pixelated source and the imaging device, wherein the diaphragm has an adjustable collection angle for an image originating in the pixelated source. The image processing calculation includes: acquiring a pixelated image of the transparent sample, the pixelated image comprising a plurality of pixels; determining boundaries between adjacent pixels in the pixelated image; integrating within the boundaries to obtain an integrated energy for each source pixel in the pixelated image; and calculating a standard deviation of the integrated energy for each source pixel, wherein the standard deviation is the power per pixel dispersion. As used herein, an “PPD₁₄₀” and “sparkle” values, attributes and limits are calculated and evaluated with a test setup employing a display device having a pixel density of 140 pixels per inch (PPI) (also referred herein as “PPD₁₄₀”).

According to some implementations of the display article 100 shown in FIGS. 1A and 1B, the substrate 10 exhibits a sparkle of less than 4%, 3.5%, 3%, 2.5%, 2%, 1.5%, 1%, 0.5, and all sparkle threshold values between the foregoing levels, as measured by PPD₁₄₀ at an incident angle of 0° from normal with a 140 ppi LCD display. For example, the substrate 10 can exhibit a sparkle of 3.5%, 3.25%, 3%, 2.75%, 2.5%, 2.25%, 2%, 1.75%, 1.5%, 1.25%, 1%, 0.75%, 0.5%, and all sparkle values between the foregoing levels, as measured by PPD₁₄₀ at an incident angle of 0° from normal.

Referring again to the display article 100 depicted in FIGS. 1A and 1B, the article can also be configured for optimal antiglare performance, as manifested by low distinctness of image (DOI) values. As used herein, “DOI” is equal to 100*(R_(s)−R_(0.3°))/R_(s), where R_(s) is the specular reflectance flux measured from incident light (at 20° from normal) directed onto the diffractive surface region 30 a of the display article 100 of the disclosure and R_(0.3°) is the reflectance flux measured from the same incident light at 0.3° from the specular reflectance flux, R_(s). Unless otherwise noted, the DOI values and measurements reported in this disclosure are obtained according to the ASTM D5767-18, entitled “Standard Test Method for Instrumental Measurement of Distinctness-of-Image (DOI) Gloss of Coated Surfaces using a Rhopoint IQ Gloss Haze & DOI Meter” (Rhopoint Instruments Ltd.). According to some embodiments of the display article 100 shown in FIGS. 1A and 1B, the substrate 10 exhibits a DOI of less than 90%, 85%, 80%, 75%, 70%, 65%, 60%, 55%, 50%, 45%, 40%, and all DOI threshold values between the foregoing levels, as measured at an incident angle of 20° from normal. For example, the substrate 10 can exhibit a DOI of 87.5%, 85%, 82.5%, 80%, 77.5%, 75%, 72.5%, 70%, 67.5%, 65%, 62.5%, 60%, 57.5%, 55%, 52.5%, 50%, 47.5%, 45%, 42.5%, 40%, and all DOI values between the foregoing levels, as measured at an incident angle of 20° from normal.

As used herein, the terms “transmission haze” and “haze” refer to the percentage of transmitted light scattered outside an angular cone of about ±2.5° in accordance with ASTM D1003, entitled “Standard Test Method for Haze and Luminous Transmittance of Transparent Plastics,” the contents of which are incorporated by reference herein in their entirety. For an optically smooth surface, transmission haze is generally close to zero. According to implementations of the display article 100 depicted in FIGS. 1A and 1B, the articles can be characterized by a haze of less than 20%. According to implementations of the display article 100 shown in FIGS. 1A and 1B, the substrate 10 can also exhibit a transmittance haze of less than 20%, 15%, 10%, 5%, and all haze threshold values between the foregoing levels, as measured at an incident angle of 0° from normal. As an example, the substrate 10 can exhibit a transmittance haze of 17%, 16%, 15%, 14%, 13%, 12%, 11%, 10%, 9%, 8%, 7%, 6%, 5%, 4%, 3%, 2%, 1%, and all haze values between the foregoing levels, as measured at an incident angle of 0° from normal.

According to some implementations of the display article 100 depicted in FIGS. 1A and 1B, the diffractive surface region 30 a of the substrate 10 can effect a reduction in specular reflectance (Rs) and absolute specular reflectance (% R). As used herein, “specular reflectance (Rs)” is defined as the total reflected light from the first surface of the substrate 10 (e.g., primary surface 12) within a cone of angles of +/−0.1°, or as the peak intensity of light within this specular angular range. Further, the Rhopoint IQ meter reports an Rs value in gloss units (GU) that is normalized to a maximum of 100 for a flat glass having an index of 1.567 illuminated at 20° angle of incidence and no back-surface reflectance. As such, a glass is known to have a first-surface absolute specular reflectance (% R) of 4.91%, Rs values in gloss units (GU) reported by the Rhopoint IQ meter can be converted to an absolute specular reflectance (% R) by multiplying by a factor of 4.91/100. As such, implementations of the display article 100 are configured such that they exhibit a reduction in the specular reflectance (Rs) or absolute specular reflectance (% R) by a factor of 2, a factor of 4, a factor of 5, or a factor of 10 or more as compared to the same surface of a substrate, but lacking the diffractive surface region 30 a. In embodiments, the substrate 10 (e.g., a glass composition having a refractive index of about 1.51), as including the diffractive surface region 30 a, can exhibit a first-surface absolute specular reflectance (% R) of less than 2%, less than 1.5%, less than 1%, less than 0.8%, less than 0.6%, less than 0.5%, less than 0.4%, or even less than 0.25%, as measured at an incident angle of 20° from normal, at wavelengths between 450 nm and 650 nm.

Referring now to FIG. 1C, a display article 100 is depicted with the same features and attributes as the display article 100 shown in FIGS. 1A and 1B, with like-numbered elements having substantially the same functions and structures. Further, the display article 100 depicted in FIG. 1C employs an antireflective coating 60 disposed on the primary surface 12 of the substrate 10, to further improve the antiglare effect of the display article 100. In embodiments, the display article 100, as depicted in FIG. 1C with an antireflective coating 60, is particularly beneficial for end use applications requiring transmittance and some degree of transmitted scattering (e.g., for display devices that include features that result in subsurface reflectance such as touch sensor layers, thin film transistor layers, indium-tin-oxide layers, and other subsurface features). In embodiments, the antireflective coating 60 is configured according to a multilayer antireflective coating or film structure, as prepared to effect antiglare, optical properties for the article employing it. As an example, the antireflective coating 60 includes a plurality of alternating low refractive index and high refractive index layers 62 and 64, respectively. In some implementations, the antireflective coating 60 can have a total of three (3) to nine (9) layers, e.g., 3 layers, 4 layers, 5 layers, 6 layers, 7 layers, 8 layers or 9 layers in total. Further, each of the low refractive index layers 62 comprises a refractive index of less than or equal to about 1.8 and about the same or greater than a refractive index of the substrate 10; and each of the high refractive index layers 64 comprises a refractive index that is greater than 1.8. In this configuration, the display article 100 can exhibit a first-surface absolute specular reflectance (% R) of less than 0.5%, less than 0.4%, less than 0.3%, less than 0.2%, or even less than 0.1%, as measured at an incident angle of 0-20° from normal. Further, according to some embodiments, the display article 100 can exhibit a first-surface absolute specular reflectance (% R) of less than 0.5%, less than 0.4%, less than 0.3%, less than 0.2%, or even less than 0.1%, as measured at an incident angle of 0-20° from normal at one or more wavelengths between 450 nm and 650 nm.

The antiglare effects afforded by the addition of the antireflective coating 60 in the display article 100 shown in FIG. 1C should be approximately additive in a proportional sense. That is, the diffractive surface region 30 a of a display article 100 shown in FIGS. 1A and 1B can lower the specular reflectance of the primary surface 12 of the substrate 10 by a factor of 10, and the addition of the antireflective coating 60 can further lower the specular reflectance by a factor of 10, leading to a reduction in the specular reflectance of the display article 100 of FIG. 1C of about a factor of 100. As such, it is believed that the display article 100, as configured according to FIG. 1C, can, according to some embodiments, exhibit a first-surface absolute specular reflectance (% R) of less than 0.1%, less than 0.08%, less than 0.06%, less than 0.05%, less than 0.04%, or even less than 0.025%, as measured at an incident angle of 0-20° from normal at one or more wavelengths between 450 nm and 650 nm.

In an exemplary embodiment, as shown in FIG. 1C, a low refractive index layer 62 of the antireflective coating 60 is disposed directly on the diffractive surface region 30 a of the primary surface 12 of the substrate 10. Further, according to the embodiment shown in FIG. 1C, a low refractive index layer 62 is disposed as the top-most layer of the display article 100 and the antireflective coating 60 has a total of five (5) layers, i.e., a multilayer structure with five (5) low and high refractive index layers: 62/64/62/64/62. Suitable materials for the low refractive index layer 62 include: SiO₂, Al₂O₃, GeO₂, SiO_(x), AlO_(x)N_(y), SiO_(x)N_(y), SiAl_(y)O_(x)N_(y), MgO and MgAl₂O₄. Suitable materials for the high refractive index layer 64 include: Al₂O₃, AlO_(x)N_(y), SiO_(x)N_(y), SiAl_(y)O_(x)N_(y), AlN, SiN_(x), Si₃N₄, HfO₂, TiO₂, ZrO₂, Y₂O₃, and diamond-like carbon. Further, the thicknesses of each of the low and high refractive index layers 62 and 64 can range from about 1 nm to about 250 nm and the total thickness of the antireflective coating 60 can range from about 5 nm to 3000 nm, 5 nm to 2500 nm, 5 nm to 2000 nm, from 5 nm to 1500 nm, from 5 nm to 1000 nm, from 5 nm to 750 nm, from 5 nm to 500 nm, from 5 nm to 450 nm, from 5 nm to 400 nm, from 5 nm to 350 nm, from 5 nm to 300 nm, from 5 nm to 275 nm, from 5 nm to 260 nm, from 5 nm to 250 nm, from 100 nm to 500 nm, from 100 nm to 400 nm, from 100 nm to 350 nm, from 100 nm to 300 nm, from 100 nm to 275 nm, from 100 nm to 250 nm, from 200 nm to 500 nm, from 200 nm to 400 nm, from 200 nm to 350 nm, from 200 nm to 300 nm, from 200 nm to 275 nm, from 200 nm to 250 nm, from 250 nm to 350 nm, from 250 nm to 340 nm, and all thickness values within the foregoing ranges.

According to some embodiments of the display article 100 depicted in FIG. 1C, the antireflection coating 60 can be configured with a scratch resistant layer. In some embodiments, the scratch resistant layer can be the farthest, middlemost or lowest high refractive index layer 64 from the substrate 10. In some implementations, the scratch resistant layer is the thickest high refractive index layer 64 in the antireflection coating 60 and may also comprise one of Si₃N₄, SiN_(x) and SiO_(x)N_(y). The scratch resistant layer can also have a physical thickness from 50 nm to 2000 nm, from 50 nm to 1000 nm, from 50 nm to 500 nm, from 50 nm to 400 nm, from 50 nm to 300 nm, from 50 nm to 200 nm, 50 nm to 150 nm, 75 nm to 175 nm, 100 nm to 160 nm, and all thickness values within the foregoing ranges.

Referring again to FIGS. 1A-1C, the substrate 10 of the display article 100 can be configured with a multi-component glass composition having about 40 mol % to 80 mol % silica and a balance of one or more other constituents, e.g., alumina, calcium oxide, sodium oxide, boron oxide, etc. In some implementations, the bulk composition of the substrate 10 is selected from the group consisting of aluminosilicate glass, a borosilicate glass and a phosphosilicate glass. In other implementations, the bulk composition of the substrate 10 is selected from the group consisting of aluminosilicate glass, a borosilicate glass, a phosphosilicate glass, a soda lime glass, an alkali aluminosilicate glass, and an alkali aluminoborosilicate glass. In further implementations, the substrate 10 is a glass-based substrate, including, but not limited to, glass-ceramic materials that comprise a glass component at about 90% or greater by weight and a ceramic component. In other implementations of the display article 100, the substrate 10 can be a polymer material, with durability and mechanical properties suitable for the development and retention of the diffractive surface region 30 a.

In one embodiment of the display article 100 depicted in FIGS. 1A-1C, the substrate 10 has a bulk composition that comprises an alkali aluminosilicate glass that comprises alumina, at least one alkali metal and, in some embodiments, greater than 50 mol % SiO₂, in other embodiments, at least 58 mol % SiO₂, and in still other embodiments, at least 60 mol % SiO₂, wherein the ratio (Al₂O₃ (mol %)+B₂O₃ (mol %))/Σ alkali metal modifiers (mol %)>1, where the modifiers are alkali metal oxides. This glass, in particular embodiments, comprises, consists essentially of, or consists of: about 58 mol % to about 72 mol SiO₂; about 9 mol % to about 17 mol % Al₂O₃; about 2 mol % to about 12 mol % B₂O₃; about 8 mol % to about 16 mol % Na₂O; and 0 mol % to about 4 mol % K₂O, wherein the ratio (Al₂O₃ (mol %)+B₂O₃ (mol %))/Σ alkali metal modifiers (mol %)>1, where the modifiers are alkali metal oxides.

In another embodiment of the display article 100, as shown in FIGS. 1A-1C, the substrate 10 has a bulk composition that comprises an alkali aluminosilicate glass comprising, consisting essentially of, or consisting of: about 61 mol % to about 75 mol % SiO₂; about 7 mol % to about 15 mol % Al₂O₃; 0 mol % to about 12 mol % B₂O₃; about 9 mol % to about 21 mol % Na₂O; 0 mol % to about 4 mol % K₂O; 0 mol % to about 7 mol % MgO; and 0 mol % to about 3 mol % CaO.

In yet another embodiment, the substrate 10 has a bulk composition that comprises an alkali aluminosilicate glass comprising, consisting essentially of, or consisting of: about 60 mol % to about 70 mol % SiO₂; about 6 mol % to about 14 mol % Al₂O₃; 0 mol % to about 15 mol % B₂O₃; 0 mol % to about 15 mol % Li₂O; 0 mol % to about 20 mol % Na₂O; 0 mol % to about 10 mol % K₂O; 0 mol % to about 8 mol % MgO; 0 mol % to about 10 mol % CaO; 0 mol % to about 5 mol % ZrO₂; 0 mol % to about 1 mol % SnO₂; 0 mol % to about 1 mol % CeO₂; less than about 50 ppm As₂O₃; and less than about 50 ppm Sb₂O₃; wherein 12 mol %≤Li₂O+Na₂O+K₂O≤20 mol % and 0 mol %≤MgO+Ca≤10 mol %.

In still another embodiment, the substrate 10 has a bulk composition that comprises an alkali aluminosilicate glass comprising, consisting essentially of, or consisting of: about 64 mol % to about 68 mol SiO₂; about 12 mol % to about 16 mol Na₂O; about 8 mol % to about 12 mol % Al₂O₃; 0 mol % to about 3 mol % B₂O₃; about 2 mol % to about 5 mol % K₂O; about 4 mol % to about 6 mol % MgO; and 0 mol % to about 5 mol % CaO, wherein: 66 mol %≤SiO₂+B₂O₃+CaO≤69 mol %; Na₂O+K₂O+B₂O₃+MgO+CaO+SrO>10 mol %; 5 mol %≤MgO+CaO+SrO≤8 mol %; (Na₂O+B₂O₃)—Al₂O₃≤2 mol %; 2 mol %≤Na₂O—Al₂O₃≤6 mol %; and 4 mol %≤(Na₂O+K₂O)—Al₂O₃≤10 mol %.

In other embodiments, the substrate 10 has a bulk composition that comprises SiO₂, Al₂O₃, P₂O₅, and at least one alkali metal oxide (R₂O), wherein 0.75>[(P₂O₅ (mol %)±R₂O (mol %))/M₂O₃ (mol %)]≤1.2, where M₂O₃═Al₂O₃+B₂O₃. In some embodiments, [(P₂O₅ (mol %)+R₂O (mol %))/M₂O₃(mol %)]=1 and, in some embodiments, the glass does not include B₂O₃ and M₂O₃═Al₂O₃. The substrate 10 comprises, in some embodiments: about 40 to about 70 mol % SiO₂; 0 to about 28 mol % B₂O₃; about 0 to about 28 mol % Al₂O₃; about 1 to about 14 mol % P₂O₅; and about 12 to about 16 mol % R₂O. In some embodiments, the glass substrate comprises: about 40 to about 64 mol % SiO₂; 0 to about 8 mol % B₂O₃; about 16 to about 28 mol % Al₂O₃, about 2 to about 12 mol % P₂O₅; and about 12 to about 16 mol % R₂O. The substrate 10 may further comprise at least one alkaline earth metal oxide such as, but not limited to, MgO or CaO.

In some embodiments, the substrate 10 has a bulk composition that is substantially free of lithium; i.e., the glass comprises less than 1 mol % Li₂O and, in other embodiments, less than 0.1 mol % Li₂O and, in other embodiments, 0.01 mol % Li₂O, and in still other embodiments, 0 mol % Li₂O. In some embodiments, such glasses are free of at least one of arsenic, antimony, and barium; i.e., the glass comprises less than 1 mol % and, in other embodiments, less than 0.1 mol %, and in still other embodiments, 0 mol % of As₂O₃, Sb₂O₃, and/or BaO.

In other embodiments of the display article 100 depicted in FIGS. 1A-1C, the substrate 10 has a bulk composition that comprises, consists essentially of or consists of a glass composition, such as Corning® Eagle XG® glass, Corning® Gorilla® glass, Corning® Gorilla® Glass 2, Corning® Gorilla® Glass 3, Corning® Gorilla® Glass 4 or Corning® Gorilla® Glass 5.

According to other embodiments, the substrate 10 of the display article 100 depicted in FIGS. 1A-1C can possess an ion-exchangeable glass composition that is strengthened by either chemical or thermal means that are known in the art. In one embodiment, the substrate 10 is chemically strengthened by ion exchange. In this process, metal ions at or near a primary surface 12 and/or primary surface 14 of the substrate 10 are exchanged for larger metal ions having the same valence as the metal ions in the glass substrate. The exchange is generally carried out by contacting the substrate 10 with an ion exchange medium such as, for example, a molten salt bath that contains the larger metal ion. The metal ions are typically monovalent metal ions such as, for example, alkali metal ions. In one non-limiting example, chemical strengthening of a substrate 10 that contains sodium ions by ion exchange is accomplished by immersing the substrate 10 in an ion exchange bath comprising a molten potassium salt such as potassium nitrate (KNO₃) or the like. In one particular embodiment, the ions in the surface layer of the substrate 10 and the larger ions are monovalent alkali metal cations, such as Li⁺ (when present in the glass), Na⁺, K⁺, Rb⁺, and Cs⁺. Alternatively, monovalent cations in the surface layer of the substrate 10 may be replaced with monovalent cations other than alkali metal cations, such as Ag⁺ or the like.

In these embodiments of the display article 100 depicted in FIGS. 1A-1C, the replacement of small metal ions by larger metal ions in the ion exchange process creates a compressive stress region 50 in the substrate 10 that extends from the primary surface 12 to a depth 52 (referred to as the “depth of layer”) that is under compressive stress. It should also be understood that a compressive stress region can be formed in the glass substrate that extends from the primary surface 14 to a depth (not shown in FIG. 1) that is comparable in nature to the compressive stress region 50. More particularly, this compressive stress at the primary surface 14 of the glass substrate is balanced by a tensile stress (also referred to as “central tension”) within the interior of the glass substrate. In some embodiments, the primary surface 12 of the substrate 10 described herein, when strengthened by ion exchange, has a compressive stress of at least 350 MPa, and the region under compressive stress extends to a depth 52, i.e., depth of layer, of at least 15 μm below the primary surface 12.

Ion exchange processes are typically carried out by immersing the substrate 10 in a molten salt bath containing the larger ions to be exchanged with the smaller ions in the glass. It will be appreciated by those skilled in the art that parameters for the ion exchange process, including, but not limited to, bath composition and temperature, immersion time, the number of immersions of the glass in a salt bath (or baths), use of multiple salt baths, additional steps such as annealing, washing, and the like, are generally determined by the composition of the glass and the desired depth of layer and compressive stress of the glass as a result of the strengthening operation. By way of example, ion exchange of alkali metal-containing glasses may be achieved by immersion in at least one molten bath containing a salt such as, but not limited to, nitrates, sulfates, and chlorides of the larger alkali metal ion. The temperature of the molten salt bath typically is in a range from about 380° C. up to about 450° C., while immersion times range from about 15 minutes up to about 16 hours. However, temperatures and immersion times different from those described above may also be used. Such ion exchange treatments, when employed with a substrate 10 having an alkali aluminosilicate glass composition, result in a compressive stress region 50 having a depth 52 (depth of layer) ranging from about 10 μm up to at least 50 μm with a compressive stress ranging from about 200 MPa up to about 800 MPa, and a central tension of less than about 100 MPa.

As the etching processes that can be employed to create the diffractive surface region 30 a of the display article 100 shown in FIGS. 1A-1C, according to some embodiments, can remove alkali metal ions from the substrate 10 that would otherwise be replaced by a larger alkali metal ion during an ion exchange process, a preference exists for developing a compressive stress region 50 in the display article 100 after the formation and development of the diffractive surface region 30 a. In other embodiments, a compressive stress region 50 can be developed in the substrate 10 prior to development of the diffractive surface region 30 a to a depth 52 sufficient to account for some loss in the depth of layer in the region 50 associated with the various treatments associated with forming the diffractive surface region 30 a, as outlined below. Alternatively, the diffractive surface region 30 a may be created by an additive or coating process rather than a substrate etching process, in which case it may be desirable to develop the compressive stress region 50 before this additive or coating process.

According to another implementation of the display article 100 depicted in FIGS. 1A-1C, the article can further include an easy-to-clean (ETC) coating (not shown) disposed over the diffractive surface region 30 a. In most embodiments, the ETC coating is deposited over the diffractive surface region 30 a such that its surface morphology generally mirrors the underlying morphology of the diffractive surface region 30 a. In one embodiment, the display article 100 further includes a smudge-resistant fluorine-based ETC coating, deposited on at least a portion of the diffractive surface region 30 a. In embodiments, the ETC coating comprises at least one amphiphobic substance having fluorine termination groups to provide the diffractive surface region 30 a with amphiphobicity (i.e., hydrophobicity and oleophobicity, or lack of affinity for both oils and water), thus minimizing wetting of the surface by water and/or oils. The fluorine termination groups of the ETC coating are less polar than a surface having OH termination groups, and therefore minimize hydrogen (i.e., Van der Waals) bonding between particles and liquids. For fingerprint oils and debris associated with fingerprints, bonding and adhesion is minimized. Consequently, mass transport of fingerprint oils and debris from the finger of a person to the ETC coating is minimized. In one embodiment, the ETC coating is formed by exchanging the hydrogen found in terminal OH groups on the diffractive surface region 30 a of the display article 100 with a fluorine-based moiety such as, for example, a fluorine-containing monomer (e.g., a fluorosilane), to form a glass having terminal fluorinated groups.

In another embodiment, an ETC coating of the display article 100 depicted in FIGS. 1A-1C comprises a self-assembled monolayer of a fluorine-terminating molecular chain. In yet another embodiment, the ETC coating comprises a thin, fluoro-polymeric coating and, in yet another embodiment, the ETC coating comprises silica soot particles that have been treated to have pendent fluorocarbon groups attached to the soot particles. Such ETC coatings can be applied to the diffractive surface region 30 a of the display article 100 by dipping, vapor coating, spraying, application with a roller, or other suitable method known in the art. After the ETC coating has been applied, it may be “cured” at temperatures ranging from about 25° C. up to about 150° C. and, in another embodiment, at temperatures ranging from about 40° C. up to about 100° C. Curing times can range from about 1 up to about 4 hours, and may be carried out in an atmosphere containing 40-95% moisture. After curing, the display article 100 with an ETC coating can be solvent rinsed to remove any unbound coating and air-dried prior to use.

Referring again to the display article 100 depicted in FIGS. 1A-1C, embodiments are configured in which the diffractive surface region 30 a includes a plurality of structural features 20 with a first portion of structural features 22 a, 22 a′ and a second portion of structural features 22 b, 22 b′. Further, the first portion of structural features 22 a (e.g., pillars), 22 a′ (e.g., holes) can be defined by a pitch 42 a of less than 125 μm, and the second portion of structural features 22 b, 22 b′ can be defined by a pitch 42 b (see FIG. 1A) substantially the same or different from the pitch 42 a. According to some implementations, the second portion of structural features 22 b, 22 b′ (e.g., ligaments, mesas) can be defined by a pitch 42 b of less than 125 μm, with the pitch 42 a substantially the same as or different from the pitch 42 b. Further, as used herein, the pitch 42 a and 42 b of the first and second portion of structural features 22 a, 22 a′ and 22 b, 22 b′ are pitch values of these features, as would be commonly understood by those of ordinary skill in the field of the disclosure. As such, the pitch 42 a and/or 42 b of the first and second portion of structural features 22 a, 22 a′ and 22 b, 22 b′, respectively, can be less than 125 μm, 110 μm, 100 μm, 90 μm, 80 μm, 70 μm, 60 μm, 50 μm, 40 μm, 30 μm, 20 μm and all pitch values between these upper thresholds of the pitch value. In embodiments, the pitch values 42 a, 42 b may have a lower threshold, e.g., the pitch values may be larger than about 2 microns, larger than 5 microns, or larger than 10 microns.

Once again referring to the display article 100 depicted in FIGS. 1A-1C, embodiments are configured such that the first or the second portion of structural features 22 a, 22 a′ (e.g., pillars or holes) or 22 b, 22 b′ (e.g., ligaments or mesas), respectively, is at a fill fraction from about 30% to 70%, with the other portion (i.e., 22 a, 22 a′ or 22 b, 22 b′) at a fill fraction of 100% minus the fill fraction of the first or second portions 22 a, 22 a′ or 22 b, 22 b′. Hence, the first portion of structural features 22 a, 22 a′ or second portion of structural features 22 b, 22 b′ of the diffractive surface region 30 a can be configured at a fill fraction from about 30% to 70%, from about 35% to 65%, from about 40% to 60%, or from about 40% to 55%. For example, the first or second portions 22 a, 22 a′ or 22 b, 22 b′ can be configured within the diffractive surface region 30 a such that they have a fill fraction of 30%, 35%, 40%, 45%, 50%, 55%, 60%, 65%, 70%, and all fill fraction levels between the foregoing values.

Still referring to the display article 100 depicted in FIGS. 1A-1C, the diffractive surface region 30 a is arranged within the primary surface 12 of the substrate 10 such that each of the plurality of structural features 20, e.g., the first and second portion 22 a, 22 a′ and 22 b, 22 b′ has a diameter 32 a, 32 b of less than 100 μm. Further, as used herein, the diameter 32 a, 32 b of the first and second portion of structural features 22 a, 22 a′ and 22 b, 22 b′ represent the effective diameter or longest width dimension of these features at their full width height maximum (FWHM), as would be commonly understood by those of ordinary skill in the field of the disclosure. As such, the diameter 32 a, 32 b of the structural features of the first and second portion 22 a, 22 a′ and 22 b, 22 b ′ can be less than 100 μm, 90 μm, 80 μm, 70 μm, 60 μm, 50 μm, 40 μm, 30 μm, 20 μm, 10 μm, and all diameter values less than the foregoing diameters.

According to some embodiments of the display article 100 depicted in FIGS. 1A-1C, the diffractive surface region 30 a is configured such that each of the structural features 20 has an aspect ratio of more than 10. Unless otherwise noted, the aspect ratio of each of the structural features 20, e.g., the first and second portion of structural features 22 a, 22 a′ and 22 b, 22 b′, is given by the average diameter 32 a, 32 b divided by the respective average height 24 a, 24 b. In some implementations, the aspect ratio of the structural features 20 of the diffractive surface region 30 a is more than 10, more than 20, more than 50, or more than 100. For example, a first portion of structural features 22 a, 22 a′ with an average diameter 32 a of 20 μm and an average height 24 a of 0.2 μm corresponds to an aspect ratio of 100. More generally, the diffractive surface region 30 a, as characterized by these aspect ratios, is substantially flat or planar, at least as viewed under ambient lighting without any magnification aids.

According to some implementations of the display article shown in FIGS. 1A-1C, the structural features 20 of the diffractive surface region 30 a can be configured according to a period 47 to effect antiglare properties. In some implementations of the display article 100, the structural features 20 of the diffractive surface region 30 a are configured with a period 47 that ranges from 1 μm to 200 μm, from 5 μm to 200 μm, from 5 μm to 150 μm, from 5 μm to 100 μm, from 5 μm to 50 μm, from 5 μm to 30 μm, from 20 μm to 150 μm, from 20 μm to 100 μm, from 10 μm to 30 μm, from 10 μm to 20 μm, and all period values between the foregoing ranges. For example, the structural features 20 can be configured with a relatively large period 47 on the order of about 100 μm (e.g., from about 70 to 200 μm) for end use applications of the display article 100 that benefit from maximizing a scattered light component near 0.3°, such as in the case where the application has a particular DOI target. Such DOI targets may require a scattered light component at or near 0.3° from the specular reflection direction, which can be enhanced by relatively large structural features 20. For end use applications for the display article 100 in which the DOI requirements are not as strict, smaller structural features 20 may be desirable, e.g., with a period 47 that ranges from about 5 to 30 μm and, according to some implementations, is semi-randomized to minimize color and/or Moire artifacts. We have found that the level and type of feature randomization in the X-Y dimension can be very important to achieving low PPD while also minimizing other display artifacts such as Moire or color banding. Put another way, traditional, perfectly ordered grating-like structures are not preferred for the articles of the disclosure. We have also found that structural features 20 that range from about 5 to 30 μm can affect DOI, and can be designed to achieve DOI values e.g. below 90 or below 80, so it is not essential to have larger structural features 20 to have some effect on DOI. The randomization of the structural features 20 at the period 47 can be characterized by a variation in nearest-neighbor distances over a distribution range which may be limited to 1.2, 1.3, 1.4 or 1.5× a minimum distance or an average distance. These smaller periods 47 can still effectively suppress specular reflection, but are believed to be more desirable to reduce artifacts such as sparkle (i.e., as measured by PPD₁₄₀) in display cover applications. In some embodiments, the period 47 can be configured to range from 5 μm to 30 μm, from 10 μm to 30 μm, and from 10 μm to 20 μm, which can lower DOI to less than 90, or even less than 80, while still maintaining desirable, low sparkle levels.

Referring now to FIG. 2, a cross-sectional, schematic view of a diffractive, antiglare structure is provided. As shown schematically in FIG. 2, a diffractive optical model can illustrate the principles of the diffractive surface region 30 a. Optical modeling calculations were performed using Gsolver©, a commercially available software package. The Gsolver© package employs a rigorous, coupled-wave analysis to find solutions for Maxwell's equations, which can govern the optical performance of a diffraction grating. In the context of developing a diffractive surface region 30 a, the Gsolver© software can be applied to a linear, rectangular diffractive antiglare structure as shown in FIG. 2. Note that the rectangular nature of the diffractive antiglare structure shown in FIG. 2 departs from the structural features 20 of the diffractive surface region 30 a in the sense that the structural features 20 can comprise pillars, holes, mesas, plateaus, polygons, and other discrete, non-rectangular shapes. Nevertheless, the calculations conducted on the schematic shown in FIG. 2 demonstrate trends and provide data that is useful in the definition of the structural features 20 of the diffractive surface region 30 a that is consistent with the principles of this disclosure. Notably, as shown in FIG. 2, the as-modeled diffractive antiglare structure has a period of 20 μm and is integrated within the surface of a glass substrate having a refractive index of 1.518 at 550 nm. Further, as shown in FIG. 2, incident light at a wavelength of 550 nm is directed against the diffractive antiglare structure at an incident angle of 20 degrees. For optimal antiglare properties, it is generally desirable to suppress the zero order reflected light (i.e., specular light).

Referring now to FIGS. 3A and 3B, plots of diffraction efficiency in reflection and transmission, respectively, as a function of structure depth for the diffractive antiglare structure depicted in FIG. 2 are provided. These plots were developed from the Gsolver© software. As shown in FIG. 3A, the diffractive antiglare structure has a period of 20 μm and structure depths ranging from 0 to 0.5 μm are modeled. Further, as shown in FIG. 3A, plots of the zero through the fifth order are shown (i.e., m=0 to 5). Notably, the zero order curve is the amplitude of the specular reflectance and, as shown in the figure, is suppressed close to 0% at a structure depth of 0.14 to 0.15 μm. In addition, the specular reflectance can be suppressed by a factor of 10 compared to flat glass over a structure depth range of about 0.12 to 0.17 μm, which corresponds to about ¼ of the wavelength of light in air. A second minimum in specular reflectance is observed at the ¾ wavelength structure depth. As shown in FIG. 3B, the amplitude of the transmitted diffracted orders for the same structure as shown in FIGS. 2 and 3A is provided. For display applications, it can be desirable to maximize the zero order, i.e., the specular transmission. Specular transmission is greater than 78% of the transmittance of flat glass at a structure depth of ˜0.15 μm, which is also the preferred depth for minimization of specular reflectance. The total transmission (considering all angles) remains close to the flat glass value, and the majority of scattered light in transmission is within 10 degrees or 5 degrees of the specular direction for preferred embodiments.

Referring now to FIGS. 4A-4C, plots of diffraction efficiency in reflection as a function of structure depth for the diffractive antiglare structure depicted in FIG. 2 at fill fractions of 15%, 30% and 70%, respectively, are provided. Notably, the diffractive structures with these fill fractions at 15%, 30% and 70% do not allow the zero order (specular) reflectance to drop to zero. This indicates that the preferred fill fraction for simple bimodal height, single material structure such as this one is close to 50%, or in the range of 35% to 65%, as modeled and depicted in FIG. 2.

Referring now to FIG. 5, a plot of diffraction efficiency in reflection as a function of structure depth for the diffractive antiglare structure depicted in FIG. 2 with varying incident light wavelengths is provided. In particular, this figure illustrates the effect of incident light wavelengths on the suppression of specular reflection, particularly at the zero order. Although the optimal structure depth varies with wavelength, as shown in FIG. 5, a single structure depth near the first ¼ wavelength minimum (at the arrow) can successfully achieve a 10× reduction in specular reflectance for all visible light wavelengths from 450 to 650 nm. This shows that broadband suppression of specular reflectance in the visible range is viable using a basic, diffractive antiglare structure as modeled in FIG. 2, with a bimodal surface height distribution.

Referring again to FIGS. 2-5, these figures generally provide guidance for the display article 100 to be configured to minimize specular reflectance while maximizing specular transmittance. Further, these figures illustrate how the depth of the diffractive antiglare structure (e.g., as serving as the general basis for the diffractive surface region 30 a) affects specular reflectance. As noted earlier, the modeled linear diffractive antiglare structure of FIG. 2 differs from the diffractive surface region 30 a of the display articles 100 shown in FIGS. 1A-1C, as the latter contains a plurality of structural features 20, such as pillars, holes, polygons and other discrete features disposed in an ordered or semi-ordered array. However, in view of the modeling of the basic diffractive structure shown in FIGS. 2-5, the height or depth of the structural features 20 of the diffractive surface region 30 a is preferably maintained from 50 to 250 nm, 75 to 225 nm, 100 to 200 nm, 120 to 190 nm or from 140 to 190 nm.

More generally, the two-dimensional array of structural features 20 of the diffractive surface region 30 a can be fabricated by many processes, such as optical lithography (photomask), ink jet printing, laser patterning and/or screen printing once the intended structure for the surface region 30 a has been defined. The selection of the process depends on the resolution of the structural features 20 (e.g., in terms of diameter and/or pitch) and the technical capabilities of the given process. In some embodiments, once the structural parameters of the diffractive surface region 30 a has been defined (e.g., pillars or holes, average heights, pitch, diameter, period, etc.), the design can be converted to a computer-aided design (CAD) file and then used with any of the foregoing processes to transfer it to a substrate 10 to create the ‘engineered’ diffractive surface region 30 a.

Referring now to FIG. 6, a schematic flow chart is provided of a method 200 of making a display article (i.e., the display article 100 shown and described in FIGS. 1A-1C). The method 200 includes: a step 202 of masking a substrate 10 comprising a thickness 13 and a primary surface 12 with a mask; a step 204 of forming a diffractive surface region 30 a within the primary surface 12 of the substrate 10; and a step 206 of removing the mask from the substrate 10. The net result of the method 200 is a display article 100, for example, as depicted in FIGS. 1A and 1B. In some embodiments, the method 200 further includes a step 208 of forming an antireflective coating 60 over the diffractive surface region 30 a, to define the display article 100 (see FIG. 1C). The diffractive surface region 30 a comprises a plurality of structural features 20 that comprises a plurality of different heights in a multimodal distribution. Further, the multimodal distribution further comprises a first portion of structural features 22 a, 22 a′ at a first average height 24 a and a second portion of structural features 22 b, 22 b′ at a second average height 24 b. In addition, the substrate 10, as fabricated according to the method 200, exhibits a sparkle of less than 4%, as measured by PPD₁₄₀ at an incident angle of 0° from normal, a DOI of less than 80% at an incident angle of 20° from normal, and a transmittance haze of less than 20% from an incident angle of 0° from normal.

According to some implementations of the method 200 depicted in FIG. 6 of making a display article 100 (see FIGS. 1A-1C and earlier description), the step 202 of masking the substrate 10 can include one or more of screen print masking, inkjet print masking and photoresist masking. In some embodiments, the step 204 of forming the diffractive surface region 30 a includes etching the primary surface 12 of the substrate 10 through the mask to form the diffractive surface region 30 a, wherein each structural feature is a hole at a depth from 50 nm to 250 nm. The step 204, for example, can be conducted by etching the substrate 10, as comprising a glass composition, with an HF/HNO₃ etchant. In embodiments, the wet etching solution employed in step 204 can consist of hydrofluoric acid (HF, 49 w/w %) and nitric acid (HNO₃, 69 w/w %) combinations with 0.1-5 v/v % HF and 0.1-5 v/v % HNO₃. Typical concentrations used to achieve 100-250 nm etching depths are 0.1 v/v % HF/1 v/v % HNO₃ to 0.5 v/v % HF/1 v/v % HNO₃ solutions. For example, etching in step 204 can be carried out using a dip or spray etch process from room temperature to about 45° C. In other embodiments, the step 204 of forming the diffractive surface region 30 a can include depositing a film on the primary surface 12 of the substrate 10 through the mask (e.g., by sputtering, evaporation, or chemical vapor deposition) to form the diffractive surface region 30 a, and each structural feature is a pillar at a height from 50 nm to 250 nm. The diffractive surface region can also be formed by masking plus ‘dry etching’, plasma-based etching, reactive ion etching, or other vacuum-based etching methods. In some embodiments, such a film can be deposited through the mask with a liquid phase silica layer or other oxide layer, followed by mask removal and lift off.

EXAMPLES

The following examples describe various features and advantages provided by the disclosure, and are in no way intended to limit the invention and appended claims.

Example 1

Referring generally to FIGS. 7A-7D, a photomask/optical lithography process was used to develop the diffractive surface region structures shown in these images. In this case, a light-sensitive polymer (i.e., a photoresist) is exposed and developed to form three-dimensional relief images on the substrate (e.g., a substrate 10). In general, the ideal photoresist image has the exact shape of the designed or intended pattern in the plane of the substrate, with vertical walls through the thickness of the resist (<3 μm for spin-coatable resists, <20 μm for dry film resists, and <15 μm for screen-coatable photoresists). When exposed, the final resist pattern is binary with parts of the substrate covered with resist while other parts are completely uncovered. The general sequence of processing steps for a typical photolithography process, as consistent with the method 200 depicted in FIG. 6, is as follows: substrate preparation (clean and dehydration followed by an adhesion promoter for spin-coatable resist, e.g., hexamethyl disilazane (HMDS), photoresist spin coat, prebake, exposure, and development (i.e., step 202), followed by a wet etching process to transfer the binary image onto glass (i.e., step 204). The final step is to strip the resist after the resist pattern has been transferred into the underlying layer (i.e., step 206). In some cases, post bake and post exposure bake steps are required to ensure resist adhesion during wet etching process.

Referring now to FIGS. 7A-7D, optical micrographs are provided of diffractive surface regions of aluminosilicate glass substrates prepared according to this example with preferred etch depths in the range of 100 to 250 nm for the holes. These diffractive surface regions were prepared according to the foregoing photomasking process, followed by an etching process. More particularly, the wet etching solution used to prepare the samples of FIGS. 7A-7D consisted of hydrofluoric acid (HF, 49 w/w %) and nitric acid (HNO₃, 69 w/w %) with 0.1-5 v/v % HF and 0.1-5 v/v % HNO₃. For this example, the concentration of the etchant employed to achieve the 100-250 nm etch depths ranged from 0.1 v/v % HF/1 v/v % HNO₃ to 0.5 v/v % HF/1 v/v % HNO₃. FIGS. 7A and 7B show two-dimensional (2D) ordered arrays of structural features of diffractive surface regions at two spatial frequencies: (a) structural features with a diameter of 12 μm with a pitch of 17 μm (FIG. 7A) (referred to as a “12-17” array); and (b) structural features with a 25 μm diameter and a pitch of 50 μm (referred to as a “25-50” array). The surfaces for the ordered arrays were designed using hexagonal packing or a square packing array with a fill fraction varying from 20 to 50%. Further, FIGS. 7C and 7D show 2D arrays of structural features of diffractive surface regions with a randomly packed structure at two spatial frequencies: (a) a 50 μm structural feature diameter with a minimum pitch of 60 μm (FIG. 7C) (referred to as a “50-60” array); and (b) a 12 μm structural feature diameter with a minimum pitch of 14 μm (referred to as a “12-14” array).

Referring now to FIG. 8, a plot is provided of etch depth as a function of etch time to form two structural features of diffractive surface regions according to this example. In this example, structural features having a diameter of 12 μm and 50 μm are etched at various etch times and the resulting etch depths are plotted (e.g., as consistent with the structures shown in FIGS. 7D and 7C, respectively). In this example, the substrate is a glass composition and it was etched with a 49 vol % stock solution of HF. Etch depth was measured using a stylus-based profilometer (with a Z depth resolution set at <5 μm, <200 μm scan, 3 regions with a 3 mg force) or a Bruker ContourGT-X white light interferometer (with a 20× or 50× objective lens, green narrow-band light, in a single field of view image). As is evident from FIG. 8, the larger structural features (i.e., those at a diameter of about 50 μm) etch faster at longer times as compared to smaller structural features (i.e., those at a diameter of about 12 μm), which allows one to engineer the diffractive surface region to have features of different sizes at different depths or heights using the same etchant and one mask.

Referring now to FIGS. 9A and 9B, plots are provided of DOI as a function of etch depth for the structural features of the diffractive surface regions depicted in FIGS. 7C and 7D above, as having different sizes and fill fractions. As shown in FIG. 9A, the DOI levels of the 50-60 array of structural features (see also FIG. 7C) at fill fractions of 36% and 50% is shown as a function of etch depth. Similarly, as shown in FIG. 9B, the DOI levels of the 12-14 array of structural features (see also FIG. 7D) at fill fractions of 20% and 50% is shown as a function of etch depth. As is evident from FIGS. 9A and 9B, both arrays of structural features demonstrate that the minimum DOI is observed at an etch depth from about 150 to 180 nm, as generally predicted or otherwise suggested by the modeling outlined earlier and shown in FIGS. 2-5.

Referring now to FIGS. 10A and 10B, plots are provided of measured PPD₁₄₀ and haze as a function of etch depth for structural features having different sizes and fill fractions from this example. As shown in FIGS. 10A and 10B, the 50-60 array of structural features (see also FIG. 7C) at fill fractions of 36% and 50% exhibits minimum PPD₁₄₀ and haze values at low etch depths of less than 0.2 μm. With regard to FIGS. 10C and 10D, plots are provided of measured PPD₁₄₀ and haze as a function of etch depth for structural features having different sizes and fill fractions from this example. As shown in FIGS. 10C and 10D, the 12-17 array of structural features (see also FIG. 7A) at fill fractions of 20% and 50% also exhibits minimum PPD₁₄₀ and haze values at low etch depths of less than 0.2 μm. More generally, FIGS. 10A-10D demonstrate that these array of structural features at periods of 60 μm and 17 μm, respectively, show that PPD₁₄₀ and haze increase as a function of etch depth. Further, the samples having a larger spatial frequency (i.e., the 50-60 array) have more of an impact on PPD₁₄₀ with increasing etch depth (see FIG. 10A), and the samples having a higher frequency (i.e., the 12-17 array) have more of an impact on haze with increasing etch depth (see FIG. 10D).

Example 2

According to this example, an array of structural features (i.e., holes) was developed on a glass substrate with depths of 0.15 μm, 0.2 μm and 0.23 μm (Samples 950, 951, 952, respectively) according to a method consistent with the principles of the disclosure. Table 1 below lists the optical properties measured on these samples, including PPD₁₄₀ (%, as measured in a display unit at 0°), transmissivity (%), haze (%, as measured in transmission at 0°), DOI (coupled, %, as measured in reflectance at 20°) and specular reflectance, Rs (coupled, %, as measured in reflectance at 20°). As is evident from Table 1, the sample (950) with an etch depth of 0.15 μm exhibits DOI<80%, PPD₁₄₀<2%, and a haze <5%, as consistent with the diffractive surface regions consistent with the disclosure. The other samples, with depths of 0.2 and 0.23 μm, do not exhibit this combination of optical properties. This illustrates the value of preferred depth ranges in achieving targeted combinations of properties, which may vary for different preferred applications.

TABLE 1 Depth DOI Rs Sample (μm) PPD₁₄₀ Transmissivity Haze (Coupled, %) (Coupled, GU) 950 0.15 1.34 92.9 4.85 76 5.9 951 0.2 1.61 92.9 8.18 93 12.5 952 0.23 1.77 92.9 9.07 97 26.1

Referring now to FIG. 11A, an optical image and surface height distribution bar of the diffractive surface region of the sample with best combination of optical properties from Table 1 (Sample 950) is provided. More specifically, the structural features of this sample (Sample 950) have a depth of about 150 nm, a fill fraction of 50%, a 12 μm feature diameter/size and a minimum pitch of 14 μm. Referring now to FIG. 11B, an angular spectra plot is provided of the samples from Table 1 in this example. More particularly, the plot of FIG. 11B shows amplitude of reflectance vs. reflectance angle for Samples 950-952. It is evident from FIG. 11B that a reduction in specular reflectance is observed for Sample 950 as compared to Samples 951 and 952. Note that the Rhopoint IQ Gloss Haze & DOI Meter reports an Rs value in gloss units (GU), as listed in Table 1, that is normalized to a maximum of 100 for a flat glass having an index of 1.567 illuminated at 20° angle of incidence and no back-surface reflectance. Such glass is known to have a first-surface absolute reflectance (% R) value of 4.91%. Thus, the Rs value reported by the Rhopoint IQ Meter can be converted to an absolute specular reflectance value (% R value) by multiplying by a factor of 4.91/100. As such, Sample 950, with an Rs amplitude of ˜6 at 0°, corresponds to a first-surface absolute specular reflectance value (% R) of 6/100*4.91%=˜0.295%.

Example 3

According to this example, samples with an array of structural features defining a diffractive surface region were made using screen printing and etching, generating pillars on a glass surface. The target pillar size/diameter was 75 μm on the screen print pattern, which after wetting with the etchant on the glass expanded closer to a diameter of about 100 μm. Further, the target pitch for these samples was 125 μm in a hexagonal pattern with a target fill fraction of 55% (the actual fill fraction was closer to 56%). The screen print pattern was made using an ink on a clean glass surface. Table 2 lists the samples made according to this example, which reflect various etch times that result in various etch depths (i.e., pillar heights), and optical properties associated with these samples (sparkle, haze, DOI and Rs). Further, as noted earlier, the first-surface specular reflectance (Rs, in gloss units (GU)) can be converted to first-surface absolute specular reflectance (% R) by multiplying them by a factor of 4.91/100. As is evident from Table 2, the optimal etch depth range in terms of the optical property measurements corresponds to ˜¼ wavelength of light in air, i.e., the samples at etch depths of 0.141 and 0.172 μm.

TABLE 2 Etch Etch % Sparkle Coupled time depth @ 140 Coupled Rs Sample ID (s) (μm) PPI % Haze DOI (GU) C17-T10a-75H-E30-Bare-C 30 0.099 2.9 0.35 78.6 41.0 C17-T10a-75H-E45-Bare-C 45 0.141 4.5 0.44 49.0 24.5 C17-T10a-75H-E60-Bare-C 60 0.172 4.9 0.44 37.3 12.7 C17-T10a-75H-E75-Bare-C 75 0.203 11.1 0.58 72.7 18.7 C17-T10a-75H-E90-Bare-C 90 0.260 13.1 0.57 89.2 27.1 C17-T10a-75H-E130-Bare-C 130 0.339 16.5 0.97 92.3 40.2 C17-T10a-75H-E145-Bare-C 145 0.396 19.5 1.19 80.5 20.5 C17-T10a-75H-E160-Bare-C 160 0.420 9.9 1.35 61.7 15.3 C17-T10a-75H-E175-Bare-C 175 0.448 9.8 1.49 62.5 30.9 C17-T10a-75H-E190-Bare-C 190 0.505 25.7 1.96 79.7 20.9 C17-T10a-75H-E205-Bare-C 205 0.531 15.9 2.06 86.1 25.6

Referring now to FIG. 12, an angular spectra plot is provided for the sample in this example with an etch depth of ˜0.172 μm (C17-T10a-75H-E60-Bare-C), with the plot depicting amplitude of reflectance vs. reflectance angle. As is evident from FIG. 12 and Table 2, the optimal etch depth for obtaining low DOI and low Rs lies in the range of 120 to 180 nm for the structural features, and the other etch depths do not exhibit this combination of optical properties.

Referring now to FIGS. 13A and 13B, optical images are provided of the diffractive surface region and structural features of the sample depicted in FIG. 12 and Table 12 with an etch depth of 0.172 μm (C17-T10a-75H-E60-Bare-C), as viewed before and after removal of the ink as part of the screen printing and etching process. As noted earlier in the description of this example, the target size/diameter of these features was about 75 μm; however, upon expansion of the ink upon drying, the actual size of the screen-printed features (i.e., the mask) ranged from 101 to 110 μm for the specific features depicted in FIG. 13A. Also, as is evident from FIG. 13B, the regions around these ink circles were etched, thus forming the pillars of this example.

Referring now to FIG. 14, a plot is provided of DOI as a function of etch depth for the structural features of this example and detailed above in Table 2. As noted earlier, the preferred etch depth is at about ¼ wavelength of light between 0.1 and 0.2 μm with regard to reductions in DOI. In addition, a second preferred etch depth in terms of DOI is located at about % wavelength of the light at an etch depth between 0.4 and 0.5 μm. The ¾ wavelength etch depth can be less desirable because of its effect on transmitted light, as shown by the higher PPD₁₄₀ values in Table 2, as well as its lesser impact on DOI as relative to the samples at the ¼ wavelength etch depth. These results are generally consistent with the previously described diffractive antiglare optical models.

Example 4

While the diffractive surface regions of the display articles of the disclosure employ structural features having a multimodal distribution of surface heights (e.g., a bimodal distribution of surface heights), embodiments of these diffractive surface regions employ spatial randomization of the features in the X-Y dimension. In this example, two X-Y pattern randomizations are employed for the diffractive surface regions—a “hard sphere” distribution and a “Poisson disk” distribution. The former hard sphere pattern design targeted structural features at approximate 50% fill fractions, and samples with structural features having 12 μm and 50 μm diameters, respectively, were prepared according to this pattern. The latter Poisson disk pattern design targeted structural features at approximate 36% fill fractions. Each of these X-Y randomization schemes can also target diffractive surface regions with structural features at different fill fractions, feature depths, and combinations with antireflective coatings. Further, as is evident from this example and noted earlier, the level and type of feature randomization in the X-Y dimension can be very important to achieving low PPD while also minimizing other display artifacts such as Moire or color banding.

X-Y pattern randomization can be defined in different ways. One method is hexagonality with FIG. 15 showing the definition of hexagonality (H). Hexagonality is a metric for quantifying locally how close a pattern is to a hexagonal lattice. For each point in the pattern, the hexagonality (H) at that point is computed using the angles of its six nearest neighbors with respect to an arbitrary axis. The mean hexagonality (H) can be defined as follows by Equation (1):

$\begin{matrix} {H = {{\frac{1}{6}{{\sum\limits_{k = 1}^{6}\; e^{6\; i\;\alpha_{k}}}}} \in \left\lbrack {0,1} \right\rbrack}} & (1) \end{matrix}$

where k=1 to 6 for the six nearest neighbor structural features to the one structural feature and α_(k) represents the angles of each of the six nearest neighbor structural features to an arbitrary axis. As such, in the context of the diffractive surface region of the display articles of the disclosure, the spatial distribution of the plurality of structural features can have a mean hexagonality (H) that ranges from 0.4 to 1.0, according to embodiments of the disclosure. As shown in FIG. 15, the variables α_(k) represent the angles of the six nearest neighbors. On a hexagonal lattice, these six angles all differ by 60 degrees (π/3 radians), therefore the exponents in the six summands differ by 2π radians and the six complex numbers in the summation are all the same. H is unity in that case. One may take the mean hexagonality (H) of the pattern as a global metric of deviation from a perfect hexagonal lattice, useful if the pattern is homogenous. A perfect hexagonal lattice has a mean hexagonality (H) of 1.0. A completely random, stationary Poisson distribution of points has a mean hexagonality (H) of approximately 0.36, or 36%. As such, according to embodiments of the display article 100 depicted in FIGS. 1A and 1B, the plurality of structural features 20 can be characterized with a non-random spatial distribution such that H ranges from 0.4 to 0.95, from 0.4 to 0.9, from 0.4 to 0.8, from 0.36 to 0.9, from 0.36 to 0.8, from 0.36 to 0.7, and all mean hexagonality (H) values and ranges between the foregoing ranges.

With further regard to the hard sphere randomization pattern, this pattern was employed in the formation of the structural features of the diffractive surface region depicted in FIGS. 7C and 7D. These patterns were generated using a molecular dynamics simulation tool (LAMMPS) to generate the pattern. A gas of “molecules” representing the features was initially placed on a two-dimensional hexagonal lattice to fix the fill fraction at 50%. Then the gas was heated and allowed to randomize in two dimensions. The molecules were endowed with a repulsive hard-sphere potential to maintain the minimum specified spacing. The example pattern in FIG. 7C has a mean hexagonality (H) of 49% (see also FIG. 15), indicating a large deviation from a regular lattice. The “12-14” and “50-60” arrays have pattern geometries that are the same: the 50-60 pattern is simply the 12-14 pattern scaled up by an overall factor of 50/12. This scaling does not impact fill fraction, hexagonality or feature distribution functions (aside from an obvious scaling of axes) but of course it does impact the optical performance of the texture. The distribution of nearest neighbor distances (defined as center-to-center spacing of features in the X-Y space) of the 12/14 pattern is shown in FIG. 16A. Its periodogram is shown in FIG. 16B. Instead of spatial frequency, the X-axis of FIG. 16B is converted to off-specular scattering angle in degrees, for an optical wavelength of 0.55 μm.

Turning to the other 50/60 array (see FIGS. 9A and 10A) has a larger distribution of nearest neighbor distances and a lower fill fraction (36%). The structural features of these samples were arranged in a Poisson disk pattern that was generated using a “dart throwing” algorithm. This algorithm ensures an absolute minimum feature spacing (60 μm in this example), but is not very efficient at filling space. The mean hexagonality (H) is lower, at 41%. The distribution of nearest neighbor distances for the 50/60 Poisson disk pattern is shown in FIG. 17A. Its periodogram is shown in FIG. 17B. Instead of spatial frequency, the X-axis of FIG. 17B is converted to off-specular scattering angle in degrees, for an optical wavelength of 0.55 μm.

As outlined herein, a first aspect of the disclosure pertains to a display article. The display article comprises: a substrate comprising a thickness and a primary surface; and the primary surface having defined thereon a diffractive surface region. The diffractive surface region comprises a plurality of structural features that comprises a plurality of different heights in a multimodal distribution. Further, the substrate exhibits a sparkle of less than 4%, as measured by pixel power deviation (PPD₁₄₀) at an incident angle of 0° from normal, a distinctness of image (DOI) of less than 80% at an incident angle of 20° from normal, and a transmittance haze of less than 20% from an incident angle of 0° from normal.

According to a second aspect, the first aspect is provided, wherein the plurality of structural features further comprises a first portion of structural features having a first average height and a second portion of structural features having a second average height.

According to a third aspect, the second aspect is provided, wherein the first average height and the second average height have a difference of from 50 nm to 250 nm.

According to a fourth aspect, the second aspect is provided, wherein the first average height and the second average height have a difference from 120 nm to 200 nm.

According to a fifth aspect, any one of the second through fourth aspects is provided, wherein the diffractive surface region further comprises a first planar region corresponding to the first average height and a second planar region corresponding to the second average height. Further, each of the first planar region and the second planar region comprises a root-mean-square (RMS) height variation of less than 50 nm.

According to a sixth aspect, the fifth aspect is provided, wherein the first and second planar regions have a total surface area that is at least 50% of a total surface area of the diffractive surface region.

According to a seventh aspect, any one of the first through sixth aspects is provided, wherein the substrate comprises a glass composition.

According to an eighth aspect, any one of the first through seventh aspects is provided, wherein the substrate further exhibits a sparkle of less than 2%, as measured by PPD₁₄₀ at an incident angle of 0° from normal.

According to a ninth aspect, any one of the first through eighth aspects is provided, wherein the substrate further exhibits a transmittance haze of less than 5% from an incident angle of 0° from normal.

According to a tenth aspect, any one of the first through ninth aspects is provided, wherein the substrate further exhibits a first-surface absolute specular reflectance (% R) of less than 1% at an incident angle of 20° from normal.

According to an eleventh aspect, any one of the first through tenth aspects is provided, further comprising an antireflective coating disposed on the primary surface of the substrate. The antireflective coating comprises a plurality of alternating high index and low index layers. Each of the low index layers comprises a refractive index of less than about 1.8, and each of the high index layers comprises a refractive index that is greater than 1.8. Further, the article exhibits a first-surface absolute specular reflectance (% R) of less than 0.1% at an incident angle of 20° from normal.

A twelfth aspect of the disclosure pertains to a display article. The display article comprises: a substrate comprising a thickness and a primary surface; and the primary surface having defined thereon a diffractive surface region. The diffractive surface region comprises a plurality of structural features comprising a pitch of less than 125 μm and a fill fraction from 30% to 70%, each structural feature comprising a diameter of less than 100 μm. Further, the substrate exhibits a sparkle of less than 4%, as measured by pixel power deviation (PPD) at an incident angle of 0° from normal, a distinctness of image (DOI) of less than 80% at an incident angle of 20° from normal, and a transmittance haze of less than 20% from an incident angle of 0° from normal.

According to a thirteenth aspect, the twelfth aspect is provided, wherein the substrate comprises a glass composition.

According to a fourteenth aspect, the twelfth or the thirteenth aspect is provided, wherein the substrate further exhibits a sparkle of less than 2%, as measured by PPD₁₄₀ at an incident angle of 0° from normal.

According to a fifteenth aspect, any one of the twelfth through fourteenth aspects is provided, wherein the substrate further exhibits a transmittance haze of less than 5% from an incident angle of 0° from normal.

According to a sixteenth aspect, any one of the twelfth through fifteenth aspects is provided, wherein the substrate further exhibits a first-surface absolute specular reflectance (% R) of less than 1% at an incident angle of 20° from normal.

According to a seventeenth aspect, any one of the twelfth through sixteenth aspects is provided, wherein a first portion of the plurality of structural features comprises pillars having a first average height from 50 nm to 250 nm.

According to an eighteenth aspect, the seventeenth aspect is provided, wherein the plurality of structural features further comprises a plurality of heights in a multimodal distribution. The multimodal distribution further comprises the first portion of structural features at the first average height and a second portion of structural features at a second average height. Further, the first portion of the distribution has a first fill fraction from 30 to 70% and the second portion of the distribution has a second fill fraction of 100% minus the first fill fraction.

According to a nineteenth aspect, any one of the twelfth through sixteenth aspects is provided, wherein a first portion of the plurality of structural features comprises holes having a first average depth from 50 nm to 250 nm.

According to a twentieth aspect, the nineteenth aspect is provided, wherein the plurality of structural features further comprises a plurality of depths in a multimodal distribution. The multimodal distribution further comprises the first portion of structural features at the first average depth and a second portion of structural features at a second average depth. Further, the first portion of the distribution has a first fill fraction from 30 to 70% and the second portion of the distribution has a second fill fraction of 100% minus the first fill fraction.

According to a twenty-first aspect, any one of the twelfth through twentieth aspects is provided, wherein the fill fraction is from 40% to 55%.

According to a twenty-second aspect, any one of the twelfth through twenty-first aspects is provided, wherein each structural feature further comprises an aspect ratio of more than 10.

According to a twenty-third aspect, any one of the twelfth through twenty-second aspects is provided, wherein the plurality of structural features further comprises a period of from 5 μm to 100 μm.

According to a twenty-fourth aspect, any one of the twelfth through sixteenth aspects is provided, further comprising an antireflective coating disposed on the primary surface of the substrate. The antireflective coating comprises a plurality of alternating high index and low index layers. Each of the low index layers comprises a refractive index of less than about 1.8 and about the same or greater than a refractive index of the substrate. Each of the high index layers comprises a refractive index that is greater than 1.8. Further, the article exhibits a first-surface absolute specular reflectance (% R) of less than 0.1% at an incident angle of 20° from normal.

A twenty-fifth aspect of the disclosure pertains to a display article. The display article comprises: a substrate comprising a thickness and a primary surface; and the primary surface having defined thereon a diffractive surface region. The diffractive surface region comprises a plurality of structural features comprising a pitch of less than 125 a fill fraction from 30% to 70%. Further, each structural feature comprises a height or depth of from 50 nm to 250 nm.

According to a twenty-sixth aspect, the twenty-fifth aspect is provided, wherein the plurality of structural features further comprises a non-random spatial distribution.

According to a twenty-seventh aspect, the twenty-fifth or twenty-sixth aspect is provided, wherein the substrate exhibits a sparkle of less than 4%, as measured by pixel power deviation (PPD₁₄₀) at an incident angle of 0° from normal, a distinctness of image (DOI) of less than 80% at an incident angle of 20° from normal, and a transmittance haze of less than 20% from an incident angle of 0° from normal.

According to a twenty-eighth aspect, any one of the twenty-fifth through twenty-seventh aspects is provided, wherein the non-random spatial distribution of the plurality of structural features comprises a mean hexagonality (II) of from greater than 0.4 to less than 1.0, wherein the hexagonality (II) of one structural feature is given by Equation (1):

$\begin{matrix} {H = {{\frac{1}{6}{{\sum\limits_{k = 1}^{6}\; e^{6\; i\;\alpha_{k}}}}} \in \left\lbrack {0,1} \right\rbrack}} & (1) \end{matrix}$

where k=1 to 6 for the six nearest neighbor structural features to the one structural feature and α_(k) represents the angles of each of the six nearest neighbor structural features to an arbitrary axis.

According to a twenty-ninth aspect, any one of the twenty-fifth through twenty-eighth aspects is provided, wherein a first portion of the plurality of structural features comprises pillars having a first average height from 50 nm to 250 nm.

According to a thirtieth aspect, the twenty-ninth aspect is provided, wherein the height of each pillar is from 120 nm to 180 nm.

According to a thirty-first aspect, any one of the twenty-fifth through twenty-eighth aspects is provided, wherein a first portion of the plurality of structural features comprises holes having a first average depth from 50 nm to 250 nm.

According to a thirty-second aspect, the thirty-first aspect is provided, wherein the depth of each hole is from 120 nm to 180 nm.

According to a thirty-third aspect, any one of the twenty-fifth through thirty-second aspects is provided, further comprising an antireflective coating disposed on the primary surface of the substrate. The antireflective coating comprises a plurality of alternating high index and low index layers. Each of the low index layers comprises a refractive index of less than about 1.8 and about the same or greater than a refractive index of the substrate. Each of the high index layers comprises a refractive index that is greater than 1.8. Further, the article exhibits a first-surface absolute specular reflectance (% Rs) of less than 0.1% at an incident angle of 20° from normal.

A thirty-fourth aspect of the disclosure pertains to a method of making a display article. The method comprises: masking a substrate comprising a thickness and a primary surface with a mask; forming a diffractive surface region within the primary surface of the substrate; and removing the mask from the substrate. The diffractive surface region comprises a plurality of structural features that comprises a plurality of different heights in a multimodal distribution. The multimodal distribution further comprises a first portion of structural features at a first average height and a second portion of structural features at a second average height. Further, the substrate exhibits a sparkle of less than 4%, as measured by pixel power deviation (PPD₁₄₀) at an incident angle of 0° from normal, a distinctness of image (DOI) of less than 80% at an incident angle of 20° from normal, and a transmittance haze of less than 20% from an incident angle of 0° from normal.

According to a thirty-fifth aspect, the thirty-fourth aspect is provided, wherein the step of masking comprises one or more of screen print masking, inkjet print masking, photoresist masking.

According to a thirty-sixth aspect, the thirty-fourth or thirty-fifth aspect is provided, wherein the step of forming comprises etching the primary surface of the substrate through the mask to form the diffractive surface region, and wherein each structural feature is a hole comprising a depth from 50 nm to 250 nm.

According to a thirty-seventh aspect, the thirty-fourth or thirty-fifth aspect is provided, wherein the step of forming comprises depositing a film on the primary surface of the substrate through the mask to form the diffractive surface region, and wherein each structural feature is a pillar comprising a height from 50 nm to 250 nm.

Many variations and modifications may be made to the above-described embodiments of the disclosure without departing substantially from the spirit and various principles of the disclosure. All such modifications and variations are intended to be included herein within the scope of this disclosure and protected by the following claims. 

What is claimed is:
 1. A display article, comprising: a substrate comprising a thickness and a primary surface; and the primary surface having defined thereon a diffractive surface region, wherein the diffractive surface region comprises a plurality of structural features that comprises a plurality of different heights in a multimodal distribution, and wherein the substrate exhibits a sparkle of less than 4%, as measured by pixel power deviation (PPD₁₄₀) at an incident angle of 0° from normal, a distinctness of image (DOI) of less than 80% at an incident angle of 20° from normal, and a transmittance haze of less than 20% from an incident angle of 0° from normal.
 2. The display article according to claim 1, wherein the plurality of structural features further comprises a first portion of structural features having a first average height and a second portion of structural features having a second average height.
 3. The display article according to claim 2, wherein the first average height and the second average height have a difference of from 50 nm to 250 nm.
 4. The display article according to claim 2, wherein the first average height and the second average height have a difference of from 120 nm to 200 nm.
 5. The display article according to claim 2, wherein the diffractive surface region further comprises a first planar region corresponding to the first average height and a second planar region corresponding to the second average height, and further wherein each of the first planar region and the second planar region comprises a root-mean-square (RMS) height variation of less than 50 nm.
 6. The display article according to claim 5, wherein the first and second planar regions have a total surface area that is at least 50% of a total surface area of the diffractive surface region.
 7. The display article according to claim 1, wherein the substrate comprises a glass substrate or a glass-ceramic substrate.
 8. The display article according to claim 1, wherein the substrate further exhibits a sparkle of less than 2%, as measured by PPD₁₄₀ at an incident angle of 0° from normal.
 9. The display article according to claim 1, wherein the substrate further exhibits a transmittance haze of less than 5% from an incident angle of 0° from normal.
 10. The display article according to claim 1, wherein the substrate further exhibits a first-surface absolute specular reflectance (% R) of less than 1% at an incident angle of 20° from normal.
 11. The display article according to claim 1, further comprising: an antireflective coating disposed on the primary surface of the substrate, wherein the antireflective coating comprises a plurality of alternating high index and low index layers, wherein each of the low index layers comprises a refractive index of less than about 1.8, and wherein each of the high index layers comprises a refractive index that is greater than 1.8, and further wherein the article exhibits a first-surface absolute specular reflectance (% R) of less than 0.3% at an incident angle of 20° from normal.
 12. A display article, comprising: a substrate comprising a thickness and a primary surface; and the primary surface having defined thereon a diffractive surface region, wherein the diffractive surface region comprises a plurality of structural features comprising a pitch of less than 125 μm and a fill fraction from 30% to 70%, each structural feature comprising a diameter of less than 100 μm, and further wherein the substrate exhibits a sparkle of less than 4%, as measured by pixel power deviation (PPD₁₄₀) at an incident angle of 0° from normal, a distinctness of image (DOI) of less than 80% at an incident angle of 20° from normal, and a transmittance haze of less than 20% from an incident angle of 0° from normal.
 13. The display article according to claim 12, wherein a first portion of the plurality of structural features comprises pillars having a first average height from 50 nm to 250 nm.
 14. The display article according to claim 13, wherein the plurality of structural features further comprises a plurality of heights in a multimodal distribution, wherein the plurality of structural features further comprises the first portion of structural features at the first average height and a second portion of structural features at a second average height, and further wherein the first portion of structural features has a first fill fraction from 30 to 70% and the second portion of structural features has a second fill fraction of 100% minus the first fill fraction.
 15. The display article according to claim 12, wherein a first portion of the plurality of structural features comprises holes having a first average depth from 50 nm to 250 nm.
 16. The display article according to claim 15, wherein the plurality of structural features further comprises a plurality of depths in a multimodal distribution, wherein the plurality of structural features further comprises the first portion of structural features at the first average depth and a second portion of structural features at a second average depth, and further wherein the first portion of structural features has a first fill fraction from 30 to 70% and the second portion of structural features has a second fill fraction of 100% minus the first fill fraction.
 17. The display article according to claim 12, further comprising: an antireflective coating disposed on the primary surface of the substrate, wherein the antireflective coating comprises a plurality of alternating high index and low index layers, wherein each of the low index layers comprises a refractive index of less than about 1.8, and wherein each of the high index layers comprises a refractive index that is greater than 1.8, and further wherein the article exhibits a first-surface absolute specular reflectance (% R) of less than 0.3% at an incident angle of 20° from normal.
 18. A display article, comprising: a substrate comprising a thickness and a primary surface; and the primary surface having defined thereon a diffractive surface region, wherein the diffractive surface region comprises a plurality of structural features comprising a pitch of less than 125 μm, a fill fraction from 30% to 70%, and further wherein each structural feature comprises a height or depth of from 50 nm to 250 nm.
 19. The display article according to claim 18, wherein the plurality of structural features further comprises a non-random spatial distribution.
 20. The display article according to claim 18, further comprising: an antireflective coating disposed on the primary surface of the substrate, wherein the antireflective coating comprises a plurality of alternating high index and low index layers, wherein each of the low index layers comprises a refractive index of less than about 1.8, and wherein each of the high index layers comprises a refractive index that is greater than 1.8, and further wherein the article exhibits a first-surface absolute specular reflectance (% R) of less than 0.3% at an incident angle of 20° from normal.
 21. A method of making a display article, comprising: masking a substrate comprising a thickness and a primary surface with a mask; forming a diffractive surface region within the primary surface of the substrate with the mask; and removing the mask from the substrate, wherein the diffractive surface region comprises a plurality of structural features that comprises a plurality of different heights in a multimodal distribution, wherein the plurality of structural features further comprises a first portion of structural features at a first average height and a second portion of structural features at a second average height, and wherein the substrate exhibits a sparkle of less than 4%, as measured by pixel power deviation (PPD₁₄₀) at an incident angle of 0° from normal, a distinctness of image (DOI) of less than 80% at an incident angle of 20° from normal, and a transmittance haze of less than 20% from an incident angle of 0° from normal. 